A high speed motor, such as, an AC induction motor, typically includes a rotor core, which typically has a substantially cylindrical, longitudinally extending body portion. The rotor core also has a rotor shaft bore and a plurality of rotor bar slots. The rotor bar slots sometimes are referred to as secondary conductor slots.
The rotor core typically is formed by a plurality of steel laminations. More specifically, each lamination is stamped from a steel sheet, and has a central opening and a plurality of spaced, radially arranged openings adjacent the lamination outer periphery. The laminations are typically arranged in a stack so that the openings at the outer periphery of the laminations are aligned to form rotor bar slots having end rings and the central openings are aligned to form the rotor shaft bore.
To complete the rotor formation process for a standard cast aluminum type rotor, rotor bars are cast in the rotor bar slots and end rings are cast at the opposing ends of the core using, for example, an aluminum casting process. The rotor bars typically extend through the slots and the end rings “short” the bars together at the ends of the rotor core. A rotor shaft extends into the rotor shaft bore and is secured to the rotor core by any suitable process, such as, for example, interference fit or keying. Such a rotor sometimes is referred to in the art as a “squirrel cage” type rotor.
It has been known that as the rotor temperature and/or speed increases, the steel rotor core expands radially at a rate and to an extent different from the expansion rate and extent of the aluminum rotor bars and end rings. This differential radial expansion results in stresses on the rotor. One high stress region of particular concern is the interface region between the rotor end rings and the rotor bars at the outermost steel core lamination. If the stresses become substantial, the end rings can break away from the rotor bars and the rotor would fail, or in some cases the rotor bar would slide out of the rotor bar slot and make the rotor to operate less efficiently than desired.
U.S. Pat. No. 4,331,895 (John D. Edick, et al.), the disclosure of which is incorporated herein by reference, discloses a squirrel cage rotor with lamination, wherein cooling ducts and passages are provided in the rotor. A first rotor section may be of standard laminations and only one type of duct section has radially extending passageways between fingers. The entire duct section is made from a plurality of laminations having such fingers radially extending from the central core portion of the individual laminations so that the radial passageways extend to the inner wall of longitudinal ventilating ducts. In the outer ends of each finger a rotor bar aperture is formed so that the finger is a casing for such rotor bar. Initially, each duct lamination has a unitary bridge at the outer periphery joining adjacent fingers to add rigidity to the fingers. The assembled stacks of laminations making the two rotor sections are then cast with molten metal, e.g., aluminum, under low pressure to form a squirrel cage. Afterward, the rotor periphery is machined to remove the unitary bridges and to open the spaces between the fingers to act as radial vent passageways. These passageways communicate with longitudinally extending vent ducts within the rotor.
U.S. Pat. No. 5,990,595 (James Robert Crowell), the disclosure of which is incorporated herein by reference, discloses rotors and methods of assembling such rotors for electric motors. In one embodiment, the rotor includes a substantially cylindrical core having substantially planar first and second end surfaces and a substantially cylindrical body portion. The rotor core body portion has first, second and third body sections. The first body section has an outer diameter less than an outer diameter of the second body section, and the third body section has an outer diameter approximately about equal to the outer diameter of the first body section. The first and third body sections sometimes are referred to as end sections or core extensions. A plurality of radially arranged rotor bar slots extend through the body portion, and a plurality of rotor bars are cast in the rotor bar slots. The rotor bar slots in the end sections have a first geometric cross-sectional shape and the rotor bar slots in the second body section have a second geometric cross-sectional shape. The rotor bar slot geometry in the end sections is selected to allow outward displacement of the rotor bars in the radial direction.
U.S. Pat. No. 6,092,277 (Mark F. Beltowski, et al.), the disclosure of which is incorporated herein by reference, discloses a method for reducing the movement of a rotor cage relative to a rotor core in a rotor assembly, such as found in a squirrel cage AC induction motor. Movement is reduced by forming a depression in a portion of a rotor bar of the rotor cage. Formation of the depression displaces rotor bar material adjacent to the depression. The displacement of rotor bar material deforms an adjacent portion of the rotor core thereby fixing the rotor cage to the rotor core. The reduction in movement between the rotor cage and the rotor core is dependent on various depression geometries, quantities and positions. The invention further includes a rotor assembly with a substantially cylindrical rotor core having longitudinally extending slots on its outer surface. A rotor bar is positioned in at least one of the slots. The rotor assembly has at least one depression formed in a rotor bar which displaces rotor bar material into the rotor core, whereby the rotor bar is substantially fixed into a desired position with respect to the rotor core.
U.S. Pat. No. 6,534,891 (Gerald B. Kliman, et al.), the disclosure of which is incorporated herein by reference, discloses an induction motor rotor comprising a rotor shaft, a rotor core, which may be solid or may include a plurality of rotor laminations, having rotor bar slots, a plurality of rotor bars extending through the rotor bar slots, and two rotor end rings brazed to the rotor bars and extending to the rotor shaft, the rotor bars and rotor end rings pre-stressing the rotor core.
U.S. Patent Publication No. 20020145357 (Yue Li, et al.), the disclosure of which is incorporated herein by reference, discloses a rotor bar cross-section and a rotor lamination slot defining an asymmetrical shape which is divided into first and second sides about a longitudinally extending centerline, with the first and second sides being asymmetrical relative to the centerline. The first longitudinal side has upper and lower portions connected by a middle portion. The upper, middle and lower portions each include a respective point on the outer periphery of the bar located farthest from the centerline. These respective points define first, second and third distances between the respective points and the centerline, with the second distance being less than either of the first and third distances. The second longitudinal side has an upper portion directly connected to a lower portion. In certain embodiments, pairs of slots are arranged “face to face” to maintain the symmetry of the rotor lamination, even though the slots or bars themselves are asymmetrical. This improves manufacturability by allowing the use of traditional rotor construction methods for symmetrical rotor slots.
Thus, a need exists for an improved motor rotor.
This invention overcomes the problems of the prior art and provides an inventive motor rotor having at least one insertable improved rotor bar.